Abstract

In this paper, we report on the measurement of J/ψ production in the dielectron channel at midrapidity (|y| < 1) in p + p and d + Au collisions at s N N = 200 from the STAR experiment at the Relativistic Heavy Ion Collider. The transverse momentum p T spectra in p + p for p T < 4 GeV/c and d + Au collisions for p T < 3 GeV/c are presented. These measurements extend the STAR coverage for J/ψ production in p + p collisions to low p T . The < p$$2\atop{T}$$ > from the measured J/ψ invariant cross section in p + p and d + Au collisions are evaluated and compared to similar measurements at other collision energies. The nuclear modification factor for J/ψ is extracted as a function of p T and collision centrality in d + Au and compared to model calculations using the modified nuclear parton distribution function and a final-state J/ψ nuclear absorption cross section.

Tmore » he inclusive J/ψ production has been studied in Pb–Pb and pp collisions at the centre-of-mass energy per nucleon pair s NN = 5.02 eV , using the ALICE detector at the CERN LHC. he J/ψ meson is reconstructed, in the centre-of-mass rapidity interval 2.5 < y < 4 and in the transverse-momentum range p < 12 GeV/c, via its decay to a muon pair. In this Letter, we present results on the inclusive J/ψ cross section in pp collisions at √s = 5.02 eV and on the nuclear modification factor R AA. he latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum p of the J/ψ. he measured R AA values indicate a suppression of the J/ψ in nuclear collisions and are then compared to our previous results obtained in Pb–Pb collisions at s NN = 2.76 eV . he ratio of the R AA values at the two energies is also computed and compared to calculations of statistical and dynamical models. he numerical value of the ratio for central events (0–10% centrality) is 1.17 ± 0.04(stat) ± 0.20(syst). In central events, as a function of p , a slight increase of R AA with collision energy is visible in the region 2 < p < 6 GeV/c. heoretical calculations qualitatively describe the measurements, within uncertainties.« less

Asymore » mmetric nuclear collisions of p + Al , p + Au , d + Au , and He 3 + Au at s N N = 200 GeV rovide an excellent laboratory for understanding particle production, as well as exploring interactions among these particles after their initial creation in the collision. We present measurements of charged hadron production dN ch/dη in all such collision systems over a broad pseudorapidity range and as a function of collision multiplicity. A simple wounded quark model is remarkably successful at describing the full data set. We also measure the elliptic flow v 2 over a similarly broad pseudorapidity range. These measurements provide key constraints on models of particle emission and their translation into flow.« less